To see where the afflicted crustaceans go... you'll need to venture out to open waters. Best to be safe by bringing along useful camping supplies. Some sealed snacks, light, fathom pole, heating packs; just the basics. You don't think you'll be out that long, hopefully, but it also pays to be prepared.

You gather up the supplies from your scout group's communal stockpile at the garage. There, you are met by Mr. Roughscales again.

“Preparing for a trip?”
”Oh, err, yes! I'm sorry we're taking up so much space, Mr.Roughscales!”
“Nah. This room is rarely used now. Business really ain't what it used to be. Where you heading?”
”I'm studying sick animals with the protien collapse, it will help me achieve a Naturalist badge.”
“I'd certainly be willing to sign off on the witnessing credentials!” He promises, helpfully. “But that's not really something Swall get... You think you can make a natural remedy out of that?”
”Some species do, like Jaxtians. I'm curious to see if it can be cured.”

The older man is quiet for a moment.

“You're going out? Into deeper water?”
”Uhm... along the coast.”
“Hopefully not be yourself, right? There was a Zhark sighted there not too long ago.”
”Oh, not alone! Hopefully, hah, it won't be there by the time of our trip.”
“Shoot the whole thing.” Mr.Roughscales warns, shaking his hand dramatically. “It's not going to be safe out there until winter when the seas get cold. You should camp inland instead. I'm sure you can find some way to get your merit badge there.”
”Oh... well... I'll postpone the trip. Thank you, Mr. Roughscales...”

You did lie to him. You feel a little bad, but you can't exactly trust anyone else to take this journey as seriously as you are. You don't want him to tell your parents, so hopefully this ends it here. Still, he seemed strongly advised against following your research. Adults can be so weirdly stubborn.